1. Field of the Invention
The present invention relates to a paper clamp device for an impact printer.
2. Description of the Prior Art
The present invention is applicable to both a back impact printer and a front impact printer, such as those disclosed in U.S. Pat. Nos. 3,585,927 and 3,732,810.
In prior art impact printers, a type belt and a plurality of hammers are used to print information on a printing paper. A problem which often occurs in these printers is that the printed lines are commonly misaligned relative to one another. This misalignment occurs because, as the printing paper is tapped with a print hammer against a type belt to print printing characters, the type belt moves the paper sideways due to the inertial forces exerted by the type belt as it moves relative to the printing paper. In order to solve this alignment problem, a clamp device is disposed in a paper path to prevent the sideways-slippage of the printing paper.
Although prior art clamp devices prevent the sideways-slippage of the printing paper so that alignment of the printing lines can be improved, the prior art clamp devices also act as a brake, thus inhibiting the feeding motion of the paper as it is fed through the printer. This braking effect causes feed apertures, located on opposite sides of the paper, to tear and become larger. A further problem with prior art clamp devices is that, when multiple printing paper having sheets of carbon paper interposed between adjacent sheets of paper is used, the printing paper on the side of the type belt is peeled. The multiple paper 18, shown in FIGS. 1 and 2 without the carbon paper, is stapled with a paper fastener 19 outside a printing area of the paper so that each piece of printing paper is not torn. However, if the number of pieces of paper is relatively large, the clamping force of the paper fastener 19 becomes weak and causes the printing paper to be carried by the type belt and torn. As a result, the feed apertures 15 of the torn paper are disengaged with a tractor on the printer, thus increasing the possibility of the paper jamming the printer.